main span number: 1 main span length: 60.0 structure length: 60.0 roadway width: 25.6 structure width: 20.1 The 23 Mile Road Bridge is located in a north-south position. The crossing is about one-quarter of a mile south of settlement of Marengo, in a rural part of the county. The girders, which serve as railings, have curved tops with an elliptical recess and six window-like recesses; corner posts have squared caps and bases. Armco guard rails are bolted to corners. Four curved concrete brackets are located at the corner of each girder near the abutments. A bridge plate is affixed to the top of northwest corner post.

Statement of Significance

This structure was presumably built by Calhoun County as a State Reward Bridge during the 1921-1922 biennium. A note on the bridge plans explains that the superstructure of the previous bridge, probably a steel truss, was to be dismantled by the contractor and piled neatly on the bank. The current structure, and one other built in 1922, are the oldest extant examples of concrete, curved top chord through-girder bridges in the survey. This bridge is eligible for the National Register under Criterion C, as one of the oldest examples of a unique engineering design which has historic integrity.